Sigma 30 1.4 wide open samples
This is how the lens looks on a D200.
Here are some samples handheld between 1/20s - 1/40s wide open at 1.4 (done with a D50)
And a 100 percent crop:
Looks very usuable to me. Seems like a good choice for low-light shooting, two stops faster than a 2.8 lens.